Among the various methods of applying concrete there may be mentioned a blasting method. Different from a casting method in which concrete is filled in a mould or frame, according to the blasting method concrete is blasted directly against walls or inclined surfaces so that it is not necessary to fabricate a mould and disassemble the same after setting of the concrete cast therein. Accordingly, the blasting method is widely used in various civil works to coat walls of tunnels or inclined surfaces of created grounds or the like. The prior art concrete blasting methods are generally classified into dry type, wet type and semiwet type. Each of these three types has specific advantages and disadvantages. More particularly, according to the wet type blasting method a fresh fluid mixture of concrete ingredients is conveyed through a conduit in the form of a pipe or hose and then blasted through a nozzle. The physical strength of the resulting concrete is higher than that formed by the dry method. However, the frictional resistance to the fresh fluid concrete mixture while it is being conveyed through the conduit is high so that it is necessary not only to use a high pressure for conveyance but also to use pressure resistant conduit. In addition, it is necessary to limit the size of the aggregate and even with a specially designed conveyer mechanism, the distance of conveyance is limited to atmost 50 to 60 meters which is too short in certain applications. Where the ratio of water to cement is selected to manifest an optimum strength, the viscosity of the freshly mixed fluid concrete becomes large. For this reason, in most field applications, the ratio of water to cement is increased to make easy the conveyance and blasting. This of course decreases the physical strength of the resulting concrete with the result that the layer of the blasted concrete tends to peel off. Moreover, due to the flow of sag of the blasted concrete, the thickness of the layers formed by blasting is limited.
On the other hand, according to the dry method the frictional resistance during conveyance is low so that the dry concrete can be conveyed with a simpler and more compact conveyer mechanism and conduit over any desired distance. Accordingly, it is possible to readily convey the dry concrete over a long distance through tunnels disposed deep in the ground. Thus, this method is suitable for many applications but it generates a large quantity of dust. Therefore, it is necessary to interrupt blasting of the concrete with relatively short periods so as to confirm the result of the blasting. This not only greatly impairs the working environment but also the strength of the resulting concrete layer is only about one half of that obtained by the wet method because it is difficult to cause cement and aggregate to intimately contact with water. Moreover, the loss of concrete material due to splash is large. According to the semiwet method which may be said an intermediate method of the wet and dry methods the water pouring position is displaced from the nozzle to an intermediate portion of the conduit. When water is added the frictional resistance of the mixture increases and since a quick setting agent is often added, the distance of displacement is limited to 5 to 6 meters from the nozzle. When this distance is increased beyond this limit, a paste like concrete mixture would adhere to the inner surface of the conduit thus clogging the same. Accordingly, the resistance to the flow increases at the end of the conduit thus greatly decreasing the advantage of the dry method. Moreover, it is difficult to thoroughly admix water and cement as in the wet method. Thus, in each case, for the purpose of improving adhesion of the applied freshly mixed fluid concrete and of decreasing splash and peel off it is necessary to incorporate a large amount of such quick or instant setting agent as sodium silicate, calcium chloride, sodium aluminate, sodium carbonate, etc.